Abstract
Refractive index measurements of separated, ultracentrifuged and dialyzed ultracentrifuged milk were used to obtain values of 0.207, 0.187 and 0.140 ml/g for the specific refraction increments of the casein complex, soluble proteins and lactose, respectively. For milk samples from individual Friesian cows, the standard deviation of the differences between solids-not-fat (S.N.F.) determined from refractive index and by the gravimetric method was 1.8% of the mean S. N. F. The predicted linear relationship between refractive index and the concentration of S. N. F. expressed as w/v was confirmed for condensed separated milk.